A pedestrian bridge touted for its pioneering construction method collapsed Thursday over a congested road near Miami, killing at least six people, crushing eight vehicles and sending survivors to the hospital.

The bridge, which weighed more than 950 tons and was still under construction, had been intended to allow Florida International University students to avoid crossing the hectic roadway that divided their campus and the nearby city of Sweetwater. But a different and chaotic scene unfolded about 1:30 p.m. Thursday, when rescue workers raced to free victims from blocks of concrete and fractured metal.

A school news release on Saturday hailed the bridge’s “first-of-its kind” construction that was supposed to reduce “potential risks to workers, commuters and pedestrians and minimizes traffic interruptions.”

It is not yet clear whether design or construction issues played a role in the bridge’s failure. Ron Sachs, a spokesman for FIGG Engineering, which designed the bridge, said he could not provide any details as to whether the construction methods were a factor in the collapse. And the director of the Miami-Dade Police Department, Juan Perez, declined to say whether stress tests had been conducted on the bridge.

Among the five deadliest bridge collapses in United States, flawed planning and execution have led to tragedy. But so have freak accidents.

Silver Bridge, between Point Pleasant, W.Va., and Gallipolis, Ohio, 1967:

December 2017 marked the 50th anniversary of the collapse of this bridge, built in 1928, which carried as many as 4,000 vehicles over the Ohio River between Ohio and West Virginia each day. The Engineering News Record in 1929 called it “the first of its type in the United States” because of its use of eyebars — 55-foot-long sections of steel — instead of steel wire cables.

While the original design of the two-lane bridge called for conventional wire cables, the eyebar chain design was chosen instead because it was cheaper, according to the West Virginia Department of Transportation. The Engineering News Record at the time ominously noted that, based on the bridge’s design, “any adjustments in the chains, hangers, or trusses after erection” would not be possible.

On Dec. 5, 1967, eyewitnesses heard a loud noise that sounded like a gunshot. In less than 20 seconds, the bridge “folded like a deck of cards,” according to the West Virginia Department of Transportation. Sixty-four people — and 32 vehicles — fell into the river, and 46 people died.

An investigation into the bridge’s collapse found it was spurred by a small stress crack inside the loop of an eyebar, brought on by corrosion, and practically impossible to detect without taking apart the entire eyebar. But taking apart the eyebar would have compromised the bridge’s structural integrity.

Laboratory work concluded that “with the north … chain thus broken, the structure’s design made total collapse … inevitable.”

The absence of the bridge connecting Ohio and West Virginia led to an economic loss of about $1 million a month, prompting President Lyndon B. Johnson in 1968 to order a federal-state program for its immediate reconstruction. The Silver Memorial Bridge connecting Gallipolis and Henderson, W.Va., was completed in 1969. It still stands.

Sunshine Skyway Bridge, Tampa Bay, Fla., 1980:

A car is halted at the edge of the Sunshine Skyway Bridge across Tampa Bay, Fla., after the freighter Summit Venture struck the bridge during a thunderstorm and tore away a large part of the span in May 1980. At least 31 people were killed, 23 of them aboard a bus that toppled into the water. (AP) (Jackie Green/ASSOCIATED PRESS)

When the freighter Summit Venture rammed into the Sunshine Skyway Bridge across Tampa Bay, Fla., in 1980, the bridge’s structures collapsed, and six cars, a truck and a Greyhound bus plunged 150 feet through steel and iron beams into Tampa Bay, according to NPR. Thirty-five people were killed.

The new Sunshine Skyway was completed in 1987 and still stands. This new bridge incorporated safer features: It was higher, for example, and the channel underneath it widened. Large concrete barriers, called “dolphins,” were installed to keep ships from hitting the bridge.

Hyatt Regency Hotel skywalks, Kansas City, Mo., 1981:

A man walks through the scattered wreckage in the lobby of Kansas City’s Hyatt Regency Hotel on July 19, 1981. Two catwalks spanning the lobby crashed onto a crowded dance floor on Friday, killing 111 people and injuring 188 others. (AP)

Decades later, there’s almost no indication at the Hyatt Regency Hotel in Kansas City, Mo., that two suspended skywalks plummeted to the hotel’s crowded lobby floor during a casual afternoon dance, as the opening bars of Duke Ellington’s “Satin Doll” played. The collapse killed 111 people and injured 188 in what is still considered the city’s bloodiest tragedy.

The collapse dropped tons of steel, concrete and glass onto dozens of dancing couples, The Washington Post reported at the time. Many of the couples were elderly, partaking in the one-year-old hotel’s regular function. The walkway had allowed about 50 people to peer down at the dancing couples from high above.

A government study conducted in February 1982 found that the 32-ton skywalks had barely supported their own weight, and that a change in the original design of the elevated walkways during their construction worsened the issue. Still, even the original design involved a “load tolerance less than that required by city codes,” according to The Post. The Post reported:

The report said that a decision during construction to change the design “further aggravated an already critical situation.” The original design had both walkways suspended from the hotel roof by a common set of rods. The design change had the fourth-floor walkway suspended by one set of rods and the second-floor walkway suspended from the walkway above it by another set.

The design change left the walkways capable of bearing only 21,400 pounds, rather than the 68,000 pounds required under the building code, according to the report.

Cypress Street Viaduct, Oakland, Calif., 1989:

“Interstate 880, Down and Out in Oakland,” read the October 1989 headline of a Washington Post story after the freeway’s Cypress Street Viaduct, described as a “concrete-and-steel leviathan,” collapsed in a 7.1 magnitude earthquake. Forty-two people were killed.

Built in 1957, the concrete roadway’s two-tier design was common in California, incorporating complex design calculations (during an era when highway engineers did not use computers) to gauge how much steel was necessary to support the structure. When the roadway collapsed, engineers and geologists determined that its collapse was inevitable.

The factors that led to the collapse, The Post reported, included the structure’s “hinge joints,” used to add flexibility to the structure:

1) “Hinge joints” were included in the freeway’s column design to absorb weight and vertical movement caused by traffic. But during the Loma Prieta quake the ground also shook laterally, creating stress the hinge joints could not withstand.

2) Few steel reinforcing rods snaked up through the joints. The upper and lower columns are honeycombed with these “rebars,” but the hinge joints contain only a few.

3) During the quake, the columns acted like weak legs on a wobbly table. The lateral movement caused them to snap outward at the weakest point — the hinge joints — freeing the upper deck to pancake down onto the lower one.

Big Bayou Canot Bridge, Mobile, Ala., 1993:

The wreckage of an Amtrak Sunset Limited train near Mobile, Ala. A barge hit a railroad bridge and minutes later the train hit the bent tracks and plunged into the bayou, killing 47 people. (AP) (Mark Foley/AP)

When Amtrak’s Sunset Limited train crossed the Big Bayou Canot Bridge in Mobile, Ala., in September 1993, the train derailed, sending three locomotives and four front cars plunging into the creek. It was about 3 a.m.

According to The Washington Post’s Mary Jordan and William Booth:

In the water, passengers floundering in the bayou could be heard yelling, warning each other, “Don’t light any matches!” as diesel fuel poured onto the water.

About 100 of the survivors filed out of the back of the train in the panic of the dark. For dozens of others, the only way to safety was jumping into the bayou, where water rose well above their heads. Twenty-seven of the 30 people in one passenger car died when it roared off the bridge and sank completely.

Forty-seven people died in the disaster.

What the train’s passengers didn’t know was that minutes before the derailment, the towboat MV Mauvilla was lugging six barges loaded with coal and cement up the river to Birmingham. It got lost in the dark and wandered into the bayou. It is suspected that one of the barges slammed into the bridge, bending the track about three feet off its center.